Great quantities of cooking oil and fats are utilized daily by cooks and food processors to prepare food. Typical cooking methods involve immersing the food to be cooked, e.g., in a wire basket, into a heated vat of cooking oil and permitting the food to remain therein until cooked. Cooking under such circumstances gives the food its own distinctive cooked flavor.
Unfortunately, as cooking oils and fats are used, there is a progressive build up of undesirable constituents such as free fatty acids. Cooking oils and fats used for frying foods are generally composed of triglycerides with minor amounts of free fatty acids. The chemical breakdown of the triglycerides, mainly caused by hydrolysis and oxidation, forms fatty acids, short chain compounds such as aldehydes, ketones and acids. If degradation proceeds to any significant extent, the degradation products impart an unacceptable flavor to the cooked foods.
As the concentration of free fatty acid builds, the cooking oil progressively assumes undesirable characteristics such as foaming, darkening, smoking, forming gums and residues and imparting distinctive interfering flavors to the food being cooked.
Some cooks and food processors merely add new cooking oil or fat to the degraded material to extend the useful life of the cooking oil. While this is temporarily effective, the problem will be repeated as additional degradation takes place. Other cooks merely discard the entire batch of cooking oil or fat and replace it with a fresh supply. Many cooks and some food processors discard their cooking oil after a scheduled use time to preserve the integrity of the flavor of their cooked food notwithstanding the fact that degradation may not have occurred to an extent to even remotely interfere with the food. The latter method causes considerable waste and the unnecessary expenditure of considerable man hours, if the cooking oil or fat is discarded prematurely.
Various methods have been devised to quantitatively or qualitatively determine the degree of degradation and/or fatty acid content, but these generally have one or more problems associated therewith. One method involves frequently monitoring the taste of the food and, when the food begins to assume an off taste, utilize that as a point at which the oil is replaced or rejuvenated. Since this method requires frequent testing the flavor of the food may vary. This method is undesirably subjective. Other methods include monitoring the color of the oil, since it darkens with degradation, either by visually observing it or by using photoelectric devices to make the observation. These methods are undesirable because they generally require the removal and handling of small volumes of hot oil. Additionally, the photoelectric examination requires relatively expensive equipment which must be maintained and is subject to failure. Another method involves titrating small samples of the oil with a standard basic solution. The titration method is undesirable because it also requires removing samples of typically hot oil and also requires the preparation of standard titration solutions and the maintenance of certain laboratory equipment for use therewith, typically not found in most restaurants and some food processing facilities. Some test methods have been devised utilizing test papers, but they have generally been unacceptable because they have not been sufficiently accurate, are difficult to use, or give misleading results.
Illustrative of the prior art dealing with testing oils, fats and the like for degradation, fatty acid content, or similar purposes are the following U.S. Patents:
Bergstrom et al U.S. Pat. No. (2,770,530), Seeman et al U.S. Pat. No. (3,030,190), Apter U.S. Pat. No. (3,615,226) and Elliott et al U.S. Pat. No. (2,953,439) disclose various "wet" methods of testing oils which require the removal of small amounts of oil from the main batch. Eiseman U.S. Pat. No. (3,238,020) discloses an oil test strip containing an indicator and an aliphatic polyhydroxy compound. Davis U.S. Pat. No. (3,420,635) discloses a fruit ripeness telltale formed of a sheet of plastic having thereon a color-changing composition including an acid-base indicator and a solid absorbent for CO.sub.2 such as calcium hydroxide to detect when the fruit is ripened and a small amount of hydroscopic material such as calcium hydroxide to detect when the fruit is ripened and a small amount of hydroscopic material such as calcium chloride to insure the presence of moisture. Pickup et al U.S. Pat. No. (3,580,704) disclose the colorimetric indicators for determining pH of motor oil with paper treated with an acid-indicator and a non-aqueous, non-volatile liquid solvent in which the oil and indicator are soluble. Matsushits U.S. Pat. No. (4,098,575) discloses a test paper impregnated with potassium iodide to determine the peroxide value of oils in fats.